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DAC filter for discrete buffer

Posted 14th August 2014 at 11:44 PM by abraxalito
Updated 22nd August 2014 at 03:56 AM by abraxalito

Here's the next experiment - a higher working impedance anti-imaging filter which allows operation without any active voltage gain stage following it. Its also one you can build with Mouser parts - Fastron make inductors suitable for this - substitute their 27mH for the 30mH for only a modest degradation in the FR. Or add a Panasonic 2.7mH in series with the 27mH if you'd like to go the whole hog.

The frequency response is -3dB at 18.5kHz and about -55dB by 24.1kHz. Passband ripple is <0.3dB.

Update - after winding all the coils I realized that I don't have a system right now to slot a full bandwidth DAC into - mine at present is fully activated. So to test out the buffer design's audible qualities I need to build a limited bandwidth DAC (for my bass/mid, up to 3.5kHz). Hence another version of the bass/mid LPF is called for, with the highest possible working impedance. Turns out I can wind a 125mH coil with wire which doesn't break too easily (0.13mm dia) so this has determined the working impedance - about 1800 ohms. Schematic attached. Now to build it - the coils will take some time as they're in the region of 700 turns each.....
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  1. Old Comment
    abraxalito's Avatar
    From Eldam:

    The fastron does not needs matching : the 5% precision is enough with your new design ?

    ...do you think it can add a big plus with a TDA1541 or TDA1387 before a i/V la SEN ?

    I think the Fastron inductors are in reality 10% and no, they are close enough (I think) that they don't need to be selected.

    About TDA1541 I think this filter won't be suitable as the output voltage will be too high. The TDA1541 has too low compliance, but the filter could be used with some additional matching resistors. Also the filter can't be used before an I/V resistor, its a voltage filter, not a current filter.
    Posted 30th August 2014 at 12:40 PM by abraxalito abraxalito is offline
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